1. Field of the Invention
The subject matter of the present invention is new aromatic bisazomethines having reactive substituents, and also a method of preparing these compounds. These new compounds are of an intense yellow to yellowish-green or orange color, and can be used particularly well as reactive pigments by virtue of their reactive groups.
2. Discussion of Prior Art
It has long been known to produce azomethines, which are referred to in the literature also as Schiff bases and have the following general formula: ##STR2## from primary amines and aldehydes or ketones, with the liberation of reaction water (e.g., benzal-aniline according to Schiff, Liebigs Annalen der Chemie, Supplement 3, 353): ##STR3##
This reaction can also be applied to bifunctional amines, in which case bisazomethines are formed with the liberation of two moles of water. If diamines, such as phenylene diamines or benzidines, are used, colored compounds are formed. For example, German Offenlegungsschrift No. 2,410,036 describes colored bisazomethines prepared from .beta.-naphthol-.alpha.-aldehydes substituted in the .gamma.-position, with phenylenediamines and unsubstituted benzidine, which are produced in a boiling mixture of ethanol and glacial acetic acid, Branch et al. (J. chem. Soc. 1964, 9, pp. 3279-90, and ibid. 6, 1965, 3706) also use a mixture of ethanol and glacial acetic acid as solvents in the preparation of bisazomethines from p-alkoxybenzaldehydes (alkyl moiety=n-C.sub.7 H.sub.15 to n-C.sub.10 H.sub.21) and halogen-, methyl- or nitro-substituted benzidines. The corresponding p-methoxybenzaldehyde is used by Barnett et al. (Chem. Commun. 17, 1971, 1002) and M. J. S. Dewar et al. (J. Org. Chem. 30, 1965, p. 3485) for the condensation with benzidines.
Also, the reaction of chloro-, methyl- and methoxy-substituted benzidines with simple and ortho-hydroxybenzaldehyde as well as 2-hydroxy-1-naphthaldehyde has already been described by several Russian authors.
It is common to all of the above-cited methods that, for the attainment of adequate yields, catalysts must be added, usually acids such as acetic acid, and that, if these are not used, only moderate yields of sometimes only 10% of the theory can be obtained. Under these circumstances, it is not possible to use aldehydes or amines having additional delicate functional groups for the condensation without their reacting with the solvent or undergoing degradation. In addition, the separation of the products from the multicomponent mixture that results involves great time and effort.
There is a strong demand on the plastics market for yellow pigments having good thermal stability, color-fastness and no tendency to bleed. The problem, therefore, existed of preparing from substituted benzidines and aromatic aldehydes and having additional functional groups so as to be suitable, after condensation to the Schiff base, for reacting under severer conditions with other functional compounds such as amines, alcohols, phenols and the like. The problem also existed of determining the correct selection of the substituents on the benzidine and aldehyde benzene nucleus and of devising a gentle method of preparing these new compounds.
In the method to be selected, the assurance must furthermore be provided that, under the given conditions, only the amino and aldehyde functions will react with one another, and that other groups needed for a subsequent condensation will remain unaltered. The method must provide a high transformation of reactant and the desired product must be easily separated from the newly-formed by-products that may still be present, so as to minimize the amount of after-processing and the attendant risk of degradation.